The present invention relates to a controller and a control method for controlling knocking which occurs in an internal combustion engine.
To date, there has been known a controller which detects the knocking phenomena which occur in an internal combustion engine by the vibration sensor (hereinafter, referred to as a knock sensor) directly attached to a cylinder block of the internal combustion engine. Since vibration of the natural frequency band according to bore size of the internal combustion engine or vibration mode of knocking occurs when knocking occurs during operation of the internal combustion engine, the controller detects knocking by measuring the vibration strength of this natural frequency.
As the characteristic of the internal combustion engine, when ignition timing is changed to the advance angle side, the output torque of the internal combustion engine increase, but knocking is easy to occur. Accordingly, the controller performs knock control which suppresses knocking by correcting ignition timing to the retard angle side in the case of detecting knocking, and suppresses drop of the output torque of the internal combustion engine by returning ignition timing to the advance angle side in the case of not detecting knocking. Ignition timing is controlled by knock control at the knock limit ignition timing which is ignition timing of most advance side of just before knocking occurs.
As technology of performing such knock control, the technology described in Japanese Patent No. 2542116 and Japanese Patent Application No. JP-A-2007-154760 is already known, for example. In the technology of Japanese Patent No. 2542116, an average value of a knock signal calculated by processing a low pass filter to the knock signal is set as a background level, a knock decision threshold is calculated by multiplying a gain and adding an offset to the background level, and occurrence of knocking is determined by comparing the knock decision threshold with the knock signal.
In the technology of JP-A-2007-154760, a median of the knock signal which was log transformed and a standard deviation of the knock signal are calculated, a background level is calculated by subtracting a value, which multiplied a constant to the standard deviation, from the median of the knock signal, and a knock occurrence intensity is calculated by dividing the knock signal by the background level.